Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to downlink or uplink transmission control with clear channel assessment in wireless communication networks with contention-based shared frequency spectrum.
Background
Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcast, or the like. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a wireless multiple-access communication system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipment (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station).
Some modes of communication may enable communications between a base station and a UE over a contention-based shared radio frequency spectrum band, or over different radio frequency spectrum bands (e.g., a licensed radio frequency spectrum band or an unlicensed radio frequency spectrum band) of a cellular network. With increasing data traffic in cellular networks that use a licensed radio frequency spectrum band, offloading of at least some data traffic to an unlicensed radio frequency spectrum band may provide a cellular operator with opportunities for enhanced data transmission capacity. An unlicensed radio frequency spectrum band may also provide service in areas where access to a licensed radio frequency spectrum band is unavailable.
Prior to gaining access to, and communicating over, a contention-based shared radio frequency spectrum band, a base station or UE may perform a listen before talk (LBT) procedure to contend for access to the shared radio frequency spectrum band. An LBT procedure may include performing a clear channel assessment (CCA) or extended CCA (eCCA) procedure to determine whether a channel of the contention-based shared radio frequency spectrum band is available. When it is determined that the channel of the contention-based shared radio frequency spectrum band is available, a channel reserving signal, such as a channel usage beacon signal (CUBS) may be transmitted to reserve the channel.
When operating on a shared radio frequency spectrum, a base station operating in a time domain duplexing (TDD) mode may indicate to other nodes, prior to or at the beginning of a frame of communications over the shared radio frequency spectrum, a TDD structure of the frame of communications. In some cases, the TDD structure may be signaled on a physical frame format indicator channel (PFFICH) and may include an indication of a downlink/uplink subframe split (or an indication of a subframe boundary at which the direction of communication switches from a downlink (DL) transmission (e.g., a transmission of DL subframes) to an uplink (UL) transmission (e.g., a transmission of UL subframes)).